/*
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you under the Apache License, Version 2.0 (the
    * "License"); you may not use this file except in compliance
    * with the License.  You may obtain a copy of the License at
    *
   *   http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.omid.tso;
  
  import org.apache.phoenix.thirdparty.com.google.common.base.Preconditions;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import javax.inject.Inject;
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * Implements the management of the state of the TSO
   */
  public class TSOStateManagerImpl implements TSOStateManager {
  
      private static final Logger LOG = LoggerFactory.getLogger(TSOStateManagerImpl.class);
  
      private List<StateObserver> stateObservers = new ArrayList<>();
  
      private TSOState state;
  
      private TimestampOracle timestampOracle;
  
      @Inject
      public TSOStateManagerImpl(TimestampOracle timestampOracle) {
          this.timestampOracle = timestampOracle;
      }
  
      @Override
      public synchronized void register(StateObserver newObserver) {
          Preconditions.checkNotNull(newObserver, "Trying to register a null observer");
          if (!stateObservers.contains(newObserver)) {
              stateObservers.add(newObserver);
          }
      }
  
      @Override
      public synchronized void unregister(StateObserver observer) {
          stateObservers.remove(observer);
      }
  
      @Override
      public TSOState initialize() throws Exception {
  
          LOG.info("Initializing TSO Server state...");
          // The timestamp oracle dictates the new state
          timestampOracle.initialize();
          long lowWatermark = timestampOracle.getLast();
          // In this implementation the epoch == low watermark
          long epoch = lowWatermark;
          state = new TSOState(lowWatermark, epoch);
  
          // Then, notify registered observers about the new state
          for (StateObserver stateObserver : stateObservers) {
              stateObserver.update(state);
          }
          LOG.info("TSO Server state {}", state);
          return state;
  
      }
  
  }